With the increasing extension of our commerce into the South American countries it is likely that more and more tropical parasitic diseases will be introduced into the United States. These will be of two types. The first will include only imported cases, in which some factor in the life history will be wanting in northern climates, and the life history of which cannot be completed here. These diseases will, of course, never get a foothold north of Mexico; they will be contracted in the tropics, although in the United States physicians will be called on to diagnose or treat the condition. The second, and far the worst type, will be the diseases for which material and conditions for the completion of their life cycle will be favorable in the United States. These are the most to be dreaded and demand the most careful consideration on the part of health officers,